1. Field of the Invention
The present invention relates to a high-frequency amplifying device that is used in a mobile communication terminal and the like and amplifies a high-frequency signal.
2. Description of the Related Art
FIG. 1 is a block diagram showing a configuration of conventional high-frequency amplifying device described in, for example, xe2x80x9cIntelligent RF Power Module Using Automatic Bias Control (ABC) System for PCS CDMA Applicationsxe2x80x9d (Sato et al., IEEE MTT-S Int. Microwave Symp. Dig. p.p.201-204, 1998). In the figure, reference numeral 201 indicates an input terminal, and 202-1 indicates a first-stage transistor for amplifying a high-frequency signal. 202-2 indicates a second-stage transistor for amplifying the high-frequency signal, and 203-1 indicates a bias feed circuit such as a distributed constant circuit, a resistor, an inductor, a capacitor or the like for biasing the input of transistor 202-1. 203-2 indicates a bias feed circuit for biasing the input of transistor 202-2, and 204-1 indicates a pull-up circuit provided on the output side of transistor 202-1. 204-2 indicates a pull-up circuit provided on the output side of transistor 202-2, and 205 indicates an output terminal, respectively.
Reference numeral 211 indicates a transistor for detecting an input signal, 212 indicates a pull-up circuit on the output side of transistor 211, and 213 indicates a comparator for comparing a reference voltage generated by a reference voltage source 214 and the voltage of signal detected by the transistor 211. Reference numeral 214 indicates the reference voltage source for generating a predetermined reference voltage, and 215 indicates a variable voltage source for applying a voltage corresponding to the result of comparison by the comparator 213 to each of the bias feed circuits 203-1 and 203-2.
The operation will next be described.
A high-frequency signal supplied via the input terminal 201 is amplified by the transistors 202-1 and 202-2 and the post-amplification high-frequency signal is output through the output terminal 205.
On the other hand, the transistor 211 detects the high-frequency signal supplied via the input terminal 201 and supplies the post-detection signal to the comparator 213. The comparator 213 compares the reference voltage generated by the reference voltage source 214 and the voltage of signal detected by the transistor 211 and supplies a signal (e.g., a signal of 0 or 1) indicative of whether the voltage of post-detection signal is higher than the reference voltage, to the variable voltage source 215. The variable voltage source 215 selects a voltage to be applied to each of the bias feed circuits 203-1 and 203-2 according to whether or not the voltage of input signal is higher than the reference voltage.
Thus the biases to be applied to the transistors 202-1 and 202-2 are changed according to the voltage (power) of input signal to reduce power consumption at low output power.
However, because the conventional high-frequency amplifying device is constructed as described above, it is accompanied by problems that a variation in gain at their changing is large and a further reduction in power consumption becomes difficult, for example, since the biases to be applied to the transistors are changed discontinuously based on whether or not the voltage of input signal is higher than the reference voltage. There is a possibility that when the variation in gain at the changing is large, a shift will occur in the phase of a signal, thus causing defective conditions upon detection. When a system, such as a W-CDMA (Wideband Code Division Multiple Access) system placed under strict constraints to a gain fluctuation band, is used in a communication apparatus or the like, it is difficult to meet such constraints when the gain variation at the changing is large.
The present invention has been made to solve the foregoing problems, therefore the present invention aims to provide a high-frequency amplifying device comprising a high-frequency amplifying unit having a one-stage amplifying element for amplifying input high-frequency signal, a measuring circuit for measuring the amplitude of input high-frequency signal, and a bias control circuit for continuously controlling a bias applied to the amplifying element according to the value of amplitude measured by the measuring circuit, whereby a steep gain variation produce by a change in the amplitude of input high-frequency signal can be suppressed.
A high-frequency amplifying device according to the present invention comprises a high-frequency amplifying unit having an amplifying element for amplifying the input high-frequency signal; a measuring circuit for measuring amplitude of the input high-frequency signal; and a bias control circuit for continuously controlling a bias applied to the amplifying element according to value of the amplitude measured by the measuring circuit. Thus an effect is obtained that a steep gain variation produce by a change in the amplitude of input high-frequency signal can be suppressed.
In accordance with the high-frequency amplifying device according to the present invention, the bias control circuit has a current adding circuit for outputting a current having a value corresponding to the amplitude measured by the measuring circuit, and a bias applying circuit for applying a bias corresponding to sum of the current output from the current adding circuit and a predetermined reference current to the amplifying element. Thus an effect is obtained that when the amplitude of input high-frequency signal becomes small, the bias can be reduced continuously and power consumption at low output power can be further reduced.
In accordance with the high-frequency amplifying device according to the present invention, the bias control circuit has a detection adjusting circuit for setting value of conducting current according to amplitude of the high-frequency signal when the measuring circuit measures the amplitude thereof. Thus an effect is obtained that an operating condition for the measuring circuit can be controlled and an adjustment of the device can be carried out with ease.
In accordance with the high-frequency amplifying device according to the present invention, the current adding circuit has a current mirror circuit for allowing a current having a value corresponding to the amplitude measured by the measuring circuit to conduct into one end thereof, and according to the current, outputting another current set based on a ratio between junction areas of the current mirror circuit and a source voltage from the other end thereof. Thus an effect is obtained that the characteristics of current to the bias applying circuit with respect to the amplitude of input high-frequency signal can be adjusted easier by adjusting the ratio between the junction areas of current mirror circuit and the source voltage thereof, and hence the bias applied to the amplifying element can be adjusted with ease.
In accordance with the high-frequency amplifying device according to the present invention, the bias applying circuit has an internal amplifying element for conducting the current output from the current adding circuit and the predetermined reference current, and the internal amplifying element and the amplifying element of the high-frequency amplifying unit constitute a current mirror circuit.
In accordance with the high-frequency amplifying device according to the present invention, the bias control circuit has a current subtracting circuit for inputting thereto a current having a value corresponding to the amplitude measured by the measuring circuit, and a bias applying circuit for supplying the current to the current subtracting circuit and applying a bias corresponding to a difference between a predetermined reference current and the current to the amplifying element. Thus an effect is obtained that it is possible to continuously increase the bias when the input high-frequency signal is reduced in amplitude, and thereby compensate for a gain reduction at low output power.
In accordance with the high-frequency amplifying device according to the present invention, the bias control circuit has a detection adjusting circuit for setting a value of conducting current according to the amplitude of high-frequency signal when the measuring circuit measures the amplitude thereof. Thus an effect is obtained that an operating condition for the measuring circuit can be controlled, and hence an adjustment of the device can easily be performed.
In accordance with the high-frequency amplifying device according to the present invention, the current subtracting circuit has a current mirror circuit for allowing a current having a value corresponding to the amplitude measured by the measuring circuit to conduct into one end thereof and according to the current, inputting another current set based on a ratio between junction areas of the current mirror circuit and a source voltage from the other end thereof. Thus an effect is obtained that the characteristics of current from the bias applying circuit with respect to the amplitude of input high-frequency signal can be adjusted easier by adjusting ratio between the junction areas of current mirror circuit and the source voltage thereof, and hence the bias applied to the amplifying element can be adjusted with ease.
In accordance with the high-frequency amplifying device according to the present invention, the bias applying circuit has an internal amplifying element for conducting the remaining current obtained by subtracting the current supplied to the current subtracting circuit from the predetermined reference current, and the internal amplifying element and the amplifying element of the high-frequency amplifying unit constitute a current mirror circuit.
In accordance with the high-frequency amplifying device according to the present invention, the measuring circuit is connected in parallel with the high-frequency amplifying unit. Thus an effect is obtained that the amplitude of high-frequency signal can be measured without degradation of the high-frequency signal supplied to the high-frequency amplifying unit.
In accordance with the high-frequency amplifying device according to the present invention, the measuring circuit, the current adding circuit and the detection adjusting circuit are connected in parallel with the high-frequency amplifying unit. Thus an effect is obtained that the measuring circuit, the detection adjusting circuit and the current subtracting circuit can be implemented in a one-chip integrated circuit, thus it makes possible to reduce the scale and cost of the device.
In accordance with the high-frequency amplifying device according to the present invention, the measuring circuit, the current subtracting circuit and the detection adjusting circuit are connected in parallel with the high-frequency amplifying unit. Thus an effect is obtained that the measuring circuit, the detection adjusting circuit and the current subtracting circuit can be implemented in a one-chip integrated circuit, thus it makes possible to reduce the scale and cost of the device.
In accordance with the high-frequency amplifying device according to the present invention, the measuring circuit has a detector circuit connected in series with the high-frequency amplifying unit, for passing a high-frequency signal to the high-frequency amplifying unit and detecting the high-frequency signal. Thus an effect is obtained that it is not necessary to additionally provide a divider for allowing the high-frequency signal to divide to the measuring circuit and the high-frequency amplifying unit, and hence a circuit scale can be reduced.